Major modes that want to integrate with tree-sitter-hl-mode should set the variable tree-sitter-hl-default-patterns. It plays a similar role to font-lock-defaults.
Minor modes that want to customize syntax highlighting should call the function tree-sitter-hl-add-patterns. It plays a similar role to font-lock-add-keywords.
The language bundle tree-sitter-langs provides highlighting queries for several languages. These queries will be used when the corresponding major modes do not set tree-sitter-hl-default-patterns.